x86/vm86: Fix the misleading CONFIG_VM86 Kconfig help text

The CONFIG_VM86 Kconfig help text is actively misleading, so fix it:

  - Don't mark it 'obsolete' in the text as we'll support the ABI as long as CPUs
    support it.

  - Qualify the part about software emulation and mention that for some apps you
    want a real vm86 mode.

  - Don't scare users away from the option, instead explain what it does.
Reported-by: Stas Sergeev <stsp@list.ru>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Austin S Hemmelgarn <ahferroin7@gmail.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Josh Boyer <jwboyer@fedoraproject.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Kconfig

@@ -1004,7 +1004,7 @@ config X86_THERMAL_VECTOR
 	depends on X86_MCE_INTEL
 
 config X86_LEGACY_VM86
-	bool "Legacy VM86 support (obsolete)"
+	bool "Legacy VM86 support"
 	default n
 	depends on X86_32
 	---help---
@@ -1016,19 +1016,20 @@ config X86_LEGACY_VM86
 	  available to accelerate real mode DOS programs.  However, any
 	  recent version of DOSEMU, X, or vbetool should be fully
 	  functional even without kernel VM86 support, as they will all
-	  fall back to (pretty well performing) software emulation.
+	  fall back to software emulation. Nevertheless, if you are using
+	  a 16-bit DOS program where 16-bit performance matters, vm86
+	  mode might be faster than emulation and you might want to
+	  enable this option.
 
-	  Anything that works on a 64-bit kernel is unlikely to need
-	  this option, as 64-bit kernels don't, and can't, support V8086
-	  mode.  This option is also unrelated to 16-bit protected mode
-	  and is not needed to run most 16-bit programs under Wine.
+	  Note that any app that works on a 64-bit kernel is unlikely to
+	  need this option, as 64-bit kernels don't, and can't, support
+	  V8086 mode. This option is also unrelated to 16-bit protected
+	  mode and is not needed to run most 16-bit programs under Wine.
 
-	  Enabling this option adds considerable attack surface to the
-	  kernel and slows down system calls and exception handling.
+	  Enabling this option increases the complexity of the kernel
+	  and slows down exception handling a tiny bit.
 
-	  Unless you use very old userspace or need the last drop of
-	  performance in your real mode DOS games and can't use KVM,
-	  say N here.
+	  If unsure, say N here.
 
 config VM86
        bool